Abstract

Precise quantification of reference evapotranspiration (ETo) is crucial for calculating crop water demand. Eight empirical methods based on temperature and six on solar radiation were evaluated against Penman-Monteith FAO 56 method based on: Mean Bias Error (MBE), Root Mean Square Error (RMSE), Willmott coefficient (“d”), determination coefficient (R2) and the Student’s t-test. The meteorological data of Vilankulo district (maximum, minimum and medium temperature, relative humidity, wind speed and sunshine hours) were used and collected in the National Institute of Meteorology of Mozambique from 1979 to 2006. The results showed that Mak solar radiation method had the best efficiency (MBE = -0.03 mm day-1; RMSE = 0.28 mm day-1; "d" = 0.97 and R2 = 0.98). When sunshine hours or global solar radiation are not measured in order to use Mak method, Schendel method can be an alternative which requires air temperature and relative humidity (MBE = -0.09 mm day-1; RMSE = 0.81 mm day-1; “d” = 0.84 and R2 = 0.74). Both methods were not statistically different with PMF 56 method. The merit of this study stems from the fact that no similar study was conducted in Vilankulo district.

Key words: Reference evapotranspiration, empirical methods, Penman Monteith.